In the art of container coating it is well known to coat both interior and exterior surface areas of a metal can of aluminum, steel or tin plate steel, for example. Prior coating materials and methods have included the spray coating of containers with conventional paints and electrophoretic coating of containers with such coating materials as water-based or water dispersible resinous coating materials. The term "electrocoating" as used herein refers to the electrodeposition of such materials on electrically conductive surface areas of a metal can from either anodic or cathodic electrocoating material or media. The metal can is confined in a cell which is then filled with a continuous flow of coating material. A layer of particulate coating material is electro-deposited on the electrically charged metal surfaces of the can as a result of an electrical potential difference maintained between the can and oppositely charged electrodes.
The prior art includes numerous examples of electrocoating technology, among these being U.S. Pat. Nos. 3,476,667, 3,922,213, 4,094,760 and 4,210,507. Inasmuch as such electrocoating of containers insofar as discussed hereinabove and disclosed in the cited prior patents is known and further description thereof is not necessary for an understanding of the present invention, additional detailed description thereof is not included hereinafter except as may be otherwise necessary for describing the invention herein.
The known apparatus for carrying out such electrocoating processes as described and cited hereinabove often has comprised a rotary turret type machine as such machines are well known in the material handling arts both for the mass manufacture of containers and for the handling of containers in the mass processing and packaging of products such as food products. In particular, known rotary turret machines have often been employed for handling metal containers for the cleansing and coating thereof during can manufacture. For example, U.S. Pat. Nos. 3,476,666, 4,026,311, 4,158,405 and 4,246,088, and British Pat. No. 1,571,808 discloses such apparatus. U.S. Pat. Nos. 3,476,666 and 4,246,088 in particular disclose the use of rotary turret type apparatus in the processing of metal cans which includes such electrically operative treatment of the cans as electrolytic surface treatment and electrodeposition of protective coating materials thereon.
In many prior rotary turret type machines for electrocoating of containers each of the containers to be coated is carried in one of a plurality of closed cells positioned around the machine circumference at equally spaced locations on a pitch circle which is coaxial with the axis of rotation of the turret machine. Accordingly, for each such turret machine a loading station and a discharge station must be provided, as well as other ancillary container handling apparatus well known in the art.
Although prior rotary turret type machines have generally served their intended purposes, they have not been without significant shortcomings. For example, in a rotary turret machine the difficulty of providing all of the electrical and fluid connections required for electrocoating processes significantly increases the complexity of the apparatus, and therefore its cost, without any compensating benefits. Each cell of the rotary turret machine must be provided with fluid connections to supply a flow of electrocoating material to each cell, and each must be provided with fluid connections for an exhaust channel to maintain the flow of coating material during the coating cycle and to drain away residual coating material at the end of the coating cycle. Additionally, motive means such as a mechanical camming action or a fluid power means for example, must be provided to open and close each cell as required during its operating cycle. Still further, means for the impression of an electrical potential difference between the container to be coated and oppositely charged electrodes must be provided for each cell.
The individual cells in a turret type machine require phased operation according to the position of each cell about the circumference of the turret at any given time. All of the cell cycle timing and the necessary control of the electrocoating material supply and exhaust, electrical connections, cell opening and closing mechanisms, and other operative entities required in the electrocoating process must be similarly phased to provide the proper cyclic operation for each cell. This requirement necessarily results in an enormously complex rotary turret type apparatus without offering compensating benefit.
The more complex a machine is, generally the more expensive and less reliable it will be than a simpler design of comparable capability. The phased relationship of the cell operating cycles in turret machines introduces considerable complexity of mechanical design and control as the cells operate neither in unison nor in a distinct sequence of cycles, either of which alternatives could be achieved in a simpler mechanical design. In turret type machines the electrocoating cycles of the several cells overlap in real time thus creating the impression of ultra high speed production. Upon reflection, however, it will be appreciated that for all its complexity of design and abundant mechanical motion, the rotary turret electrocoating machine is basically a one-at-a-time processor which is fed a can for electrocoating thereof, cycles the can through a timed electrocoating cycle, and then discharges the can for further processing.
An additional shortcoming of rotary turret type apparatus is that each machine design is highly specialized, and such machines thus lack flexibility. Each different application thus requires a custom-designed machine.
For the above and other reasons, the rotary turret type apparatus has not proven to be entirely satisfactory, although its acceptance in the manufacture of metal cans and in the canning industry is widespread.
Other shortcomings of the prior art of electrocoating apparatus include the coordination of container and cell motion during the electrocoating cycle. Typically, the prior art has required transfer of the container on at least two axes to first position the container in coaxial alignment with the cell and then to bring the probe-nozzle portion of the cell into its operative position within the interior of the container. Thus, the prior container handling apparatus, as well as the prior electrocoating apparatus which cooperates therewith, have been of considerable complexity.